1. Field of the Invention
The present invention generally relates to a spectroscopic imaging apparatus in which information concerning a distribution condition of an element, e.g., .sup.31 P and .sup.13 C within a tissue of a human body is displayed so as to represent, as an image of physiological data, whether or not there is a disease portion therein. More specifically, the present invention is directed to a spectroscopic imaging apparatus capable of displaying an additional image for compensating for unclear physiological information specific to the spectroscopic image.
2. Description of the Related Art
In a spectroscopic imaging apparatus known in the art, various physiological information concerning the presence of a nuclear species, e.g., .sup.31 P (phosphorus-31), its distribution, or a ratio of this species and a compound within a certain region of an object under examination, i.e., a tissue of a human body, is displayed as a spectroscopic image and a spectroscopic graph.
For instance, 31P(phosphorus-31) is present within a tissue of a biological body in various forms, namely PC.gamma. (phosphocreatine), PD(phosphodiester), PM(phosphomonoester), Pi(inograric phosphate), a compound such as .alpha. phosphorus nuclei of ATP (adenosinetriphosphate), .beta. phosphorus nuclei of ATP, and .gamma. phosphorus nuclei of ATP.
When .sup.31 P is employed as the nuclear species under examination, the spectroscopic image represents how phosphorus-31 is distributed as a whole within a selected tomographic (slice) region of the biological body under examination. Also, the spectroscopic graph represents the presence (abundance) ratio of the above-described various compounds involving .sup.31 P with respect to a partial region selected from the above slice region based upon a so-called "chemical shift" phenomenon.
Such a spectroscopic imaging apparatus is known from, for instance, "Chemical Shift Imaging" of a monthly magazine "NMR IGAKU (medical engineering)" Vol. 6, No. 4, 1984, on pages 221 to 239. Great developments are very much desired in the spectroscopic imaging apparatus for providing more detailed physiological information of a biological body under examination.
In the above-described conventional spectroscopic imaging apparatus, the matrix element number of the displayed spectroscopic image corresponding to the resolution is not so large, e.g., 4.times.4 to 32.times.32.
In FIG. 1, for instance, the matrix element number of the spectroscopic image is selected to be 6.times.6.
It should be noted that the above-described matrix element number is completely different from a pixel functioning as a basic display unit. In fact, the spectroscopic image "P.sub.1 " shown in FIG. 1 is displayed in 160.times.160 pixel numbers. In other words, one matrix element of the object under examination is displayed by 160/6 pixel elements in an enlarged form. However, the resolution of the pixel-enlarged spectroscopic image "P.sub.1 " is not changed, i.e., still low.
The reason why the matrix element number of the spectroscopic image is small, is that the signal-to-noise ratio thereof will be lowered if the matrix element number is selected to be large, because an amount of existence of, for instance, .sup.31 P within the tissue of the biological body is small and thus the signal level of the acquired MR (magnetic resonance) signal is also low.
In addition, the spectroscopic graph "P.sub.2 ", for instance, shown in FIG. 1, represents how the specific nuclear species, e.g., .sup.31 P is present in the specific compound at the specific presence ratio within a single matrix element constituting the spectroscopic image. A matrix element of the displayed spectroscopic graph is designated by way of a light pen or a ROI (region of interest) mark.
However, in this case, since the image resolution of the spectroscopic image is low, it is very difficult to precisely designate the matrix element to be displayed. For instance, even if an eye portion of a biological body is desired to be displayed as the spectroscopic graph, and thus the matrix element of the spectroscopic image corresponding to the eye portion is designated by the light pen (see element 70 of FIG. 2) it is practically rather difficult to achieve a clear designation of the eye portion in the displayed spectroscopic image.
In other words, even though the detailed information on the presence conditions of the specific species could be obtained, the conventional spectroscopic imaging apparatus would merely disclose a part of the detailed physiological information, namely, the distribution information of the specific species over the entire measurement region.